Skin treatment apparatus is known in the art for treatment of, for example, cosmetic purposes such as hair depilation, minimisation of skin blemishes or skin rejuvenation, as well as dermatological treatment of skin conditions such as acne or rosacea. The skin is exposed to dosages of radiation such as from a laser source or light source where the radiation is targeted to the skin and the energy intensity and pulse duration is controlled. In hair depilation, the radiation source is targeted to cause heating of the hair root causing the hair root to die.
Apparatus for use in treating the skin using intense pulsed light (IPL) in particular is now increasingly available for non-professional use, i.e., for the consumer market. Accordingly, there is an associated risk of side effects to the skin through misuse. This may be in the form of skin irritation and pain through the effect of burning or pigment change.
GB2496895 discloses an apparatus including a light source, a control unit and a base unit. The control unit removably docks from the base and comprises a sensor which can detect skin tone. This control unit is therefore positioned on the skin and detects the skin tone and is then replaced into the base unit wherein the base unit then determines the power level of radiation to be generated by the light source. The head unit (20) is then repositioned onto the skin at the location for which the skin tone has been determined and the skin is treated with a pulse of light without the requirement for the user to select an energy level output. This means that the step of the user selecting the energy to be output from the light source is removed thus reducing the potential harmful effect of a user misusing the apparatus.
WO002/085229 also discloses a device for treating skin by means of radiation pulses such as a laser source. The aim of the invention disclosed in WO02/085229 is again to reduce undesirable side effects on the skin such as skin irritation and pain through misuse of the device. This is achieved through detecting a biophysical property of the skin such as the skin tone. The device comprises a housing (3) which is portable and can be placed on or moved over skin (7) to be treated. The housing (3) accommodates a radiation source, in particular a laser source (9) such as a laser diode. The housing is positioned on the skin and an image is recorded of the part of the skin situations directly in front of an exit opening (15). The positions of the hair root (39) of the hairs (41) are determined and the laser source (9) is manipulated in order that the hair roots (39) are successively heated in such a manner that they die. Protection against an impermissible overdose of the laser pulse, however, is achieved by using a detector (43) which detects, for example, the temperature of the skin resulting from exposure to a series of test laser pulses. The detector measures the temperature of the skin after each pulse to ensure that a maximum temperature is not exceeded. In such a manner the permissible dose of energy from a laser source is controlled.
WO02/085229 discloses a further embodiment wherein a detector is utilised which measures the scattering coefficient and/or absorption coefficient of the skin for light of a predetermined wavelength and the pulse dose is determined by means of the scattering coefficient and/or absorption coefficient of the skin.
There are problems associated with the prior art arrangements. GB2496895 determines the light energy pulse dependent upon skin tone, however, relies on a user then repositioning a treatment head onto a correct location for which the skin tone has been determined. It is unlikely that positioning of the treatment head accurately reflects the positioning of the detector thus giving the possibility of incorrect output energy. Further, there is significant time delay between sensing the skin tone and the time of the treatment. WO02/085229 overcomes the problem of inaccurate positioning of the treatment head by utilising a head which incorporates both a detector for detecting a parameter of the skin such as temperature, scattering coefficient and/or absorption and treats the skin dependent on this outcome. Whilst this is possible when utilising a laser pulse there are distinct safety issues associated with the use of laser pulses.
Referring to FIGS. 1A-1C a prior art system is schematically presented as a block diagram showing how an IPL system functions. FIG. 1A identifies components in a prior art system and includes an energy storage device (20), typically comprising a capacitor, is arranged to release energy to the flashlamp (22) which in turn outputs a pulse of light energy to the skin under operation of the lamp trigger circuit (24). The energy storage device (20) is charged by a charge circuit (26) where the charge circuit (26) and lamp trigger circuit (24) are under operation of the control circuit (28). A user input (30) is provided such as a trigger which is depressed to enable the control circuit (28) to cause actuation of the lamp trigger circuit (24) causing release of charge from the energy storage device (20) to the flashlamp (22). In order to control the value of energy stored by the energy storage device (20) an input is provided to the control circuit (28) which is either from a sensor (32) arranged to measure a skin parameter such as skin tone as represented in FIG. 1A or by a user selected input described in more detail with respect to FIG. 1B.
Represented in FIG. 1B is a schematic representation of the change over time of the light output, the user input, the capacitor voltage and the capacitor charging. Prior to time T1 a user turns the apparatus on and the output power required for treatment of the skin is determined. In most prior art systems this is determined by a user visually comparing their skin tone against a chart and manually selecting a power level. In GB2496895 this is determined by a control unit having a sensor to determine the preferred power output dependent on the skin tone thereby removing the requirement for the user to make a comparison with a known scale. At T1 the control circuit (28) charges the capacitor during which time the capacitor voltage increases until T2 is reached. The time between T2 and T3 represents the time in which the capacitor is charged until the user operates the user input (30) between T3 and T4. At T4 the charge on the capacitor is released to the flashlamp and the light pulse is released onto the skin as represented by the curve between T4 and T5. The cycle is repeated as necessary on another area of skin.
FIG. 1C presents the change in light intensity over time dependent on the power output required. As such if the sensor or manual user input requires a power output of 7 J/cm2 then the capacitor is charged to 400V. Alternatively, if the skin tone is fair or light, then an energy output of 5 J/cm2 may be more appropriate and the capacitor is charged to a voltage of 338V.
The applicant has realised that there are significant limitations associated with prior art arrangements. The significant time delay associated with sensing a skin parameter such as the skin tone, subsequently charging the capacitor on the basis of the skin tone and causing energy release from the capacitor gives a significant delay to a user causing uncertainty in a user's mind as to whether the apparatus is actually operated correctly and further meaning that it is possible and likely that the apparatus has actually been moved relative to the skin before the energy pulse is discharged. This could lead to safety implications where the device was removed from the skin and was still enabled to discharge the energy. Accordingly, as described in FIG. 2, the applicant has determined that the capacitor voltage could be changed continuously or at regular time intervals on the basis of a changing measured sensor output whereby the skin tone reading is continuously or regularly being taken. This means that the effect of a user moving the apparatus before actuation of the user input would be mitigated. This would also mean that the energy stored ready for discharge by the energy storage device would be continuously adjusted, (charged or discharged) corresponding to the latest skin tone reading. This is presented in FIG. 2 showing how the sensor measures different skin tone across the skin.